Antenna



July 18, 3.939. p, s. CARTER 2,166,750

ANTENNA Filed Feb, l5, 1936 f//af/ mmf/Jar l Afm/1w j@ 6 f +17 M /6` 7+/f9 @20 fio Patented July 18, 1939 UNITED STATES PATENT OFFICE ANTENNAof Delaware Application February 15, 1936, Serial No. 64,021

14 Claims.

This invention relates to antennas, and particularly to an antenna forbroadcasting horizontally polarized waves uniformly in all horizontaldirections.

In broadcasting at extremely short wave lengths, such as when usingtelevision, it is desirable to use horizontally polarized Waves. 1t isalso required, in such case, that radiation be substantially equal inall horizontal directions. These desiderata cannot be achieved by usingthe well known simple horizontal linear radiator which produces aradiation pattern in the form of a gure 8. A small loop antenna is alsoundesirable because it gives poor efficiency and low latitudinalconcentration, although it does give equal radiation in all horizontaldirections.

The present invention provides a highly desirable type of antenn-a whichmakes possible substantially equal radiation in the horizontal planewith considerable latitudinal concentration.

I have found that for a horizontal circular loop with a given current,the field strength of the radiated wave in a horizontal direction isproportional to the irst order Bessel function of the first kindJ1(21ra/A) with the argument (21a/) wher-e a is the radius and A thewavelength. The eld is therefore a maximum when J1(21ra/}\) is a maximumor minimum. The invention is based on an understanding of thisprinciple, and em- 30 ploys one or more concentric horizontal loopshaving radii which are maxima or minima of the function J1 21ra/According to one embodiment of the invention, there is employed an arrayof concentric loops 35 broken up by series condensers, the radii ofthese loops corresponding to maximums and minimums of the first orderBessel function of the first kind J1(21ra/ successive radii havinglengths approximately equal to 0.29, 0.85, 1.36, 1.86 etc., wavelengths.Condensers are employed at proper intervals in the loop to provideuniform current distribution. Adjacent loops are energized in phaseopposition.

A better understanding of the inventionmay be had by referring to thefollowing detailed description which is accompanied by drawing, wherein:

Figs. 1 to 6, inclusive, illustrate different embodiments of theinvention.

Fig. 1 shows a single radiator consisting of a single turn horizontalloop I with four or more series condensers c, c and having a radiusequal to 0.29 wavelength, the rst maximum of the first order Besselfunction above named. Conu densers c, c partially tune the selfinductance (Cl. Z50- 33) of the loop and enable the current in differentparts of loop I to be in phase and of nearly equal amplitude. Thelengths of the wire sections between condensers are made not greaterthan onehalf Wavelength. wire sections may be made not to exceedonequarter wavelength in order to obtain substantially equal currents atall points.

Fig. 2 shows an array of concentric loops I, I', l in the samehorizontal plane, having radii respectively, of 0.29, 0.85 and 1.36wavelengths. These radii are of such values as to make the Besselfunction of the rst kind, i. e., J1(21ra/)\) a maximum or a minimum.Successive loops are energized in phase opposition, as shown, and thusproduce a system which gives a considerab-le increase in lattudinalconcentration of radiation over that of Fig. l. The spacings betweenradiator loops give maximum ield strength of the radiated wave in allhorizontal directions.

Fig. 3 shows several single loops of the type shown in Fig. 1, placedone above the other in pancake style and energized cophasally in orderto obtain greater concentration of radiation latitudinally. If desired,several of the arrays shown in Fig. 2 may be arranged in the samemanner. These loops are spaced ordinarily at least onehalf wavelengthapart.

Fig. 4 shows a modification where the circular loop is broken up intoseveral distinct radiating elements 2, 3, 4, 5 and 6, each energized bya separate feed line I5. Fig. 5 is a further modification Whereindistinct radiating elements 1, 8, 9, I0 and Il around a circle areconnected in series through folded line sections I2 of proper length togive approximately uniform current in the same direction around thecircle in all radiating elements. In these two figures the radii of theloops should be in accordance with the principles hereinabove set forthfor best operation. In each of the cases of Figs. 4 and 5 in the mannershown in the drawing, the length of each radiating element should in nocase exceed onehalf wave, irrespective of the length of the radius, inorder to prevent phase reversal of the current.. in a. radiator.

Fig. 6 shows a still further embodiment disclosing still another way offeeding separated radiating elements I6, I1, I8, I9, 20, 2l, 22, 23, 24,and 25. Here also each of these elements should not be greater thanone-half wavelength.

If desired, arrays of systems like Figs. 4, 5 and 6 may be stacked oneabove the other in the same manner as shown in Fig.` 3. It is evidentthat If desired, the lengths of the where a suflcient number ofradiating elements u like those shown in Figs. 4, 5 and 6 are employed,the individual elements may be straight instead of curved and thus theloop will depart from a true circle. In the systems of Figs. 4, 5 and 6it is important that the currents in al1 the radiating elements travelalong the circle in the same direction. The instantaneous polaritiesindicated on these figures indicate one manner in which these elementsshould be energized to effect this result. If the radius of the circlein the systems of Figs. 4, 5 and 6 is substantially 0.29 wavelength,then it is preferred that there be four separated radiating elements. Ifthe radius of the circle is 0.85 wavelength, it is preferred that therebe eleven separated radiating elements, and in the case of a radius of1.36 wavelengths it is preferred that the number of elements beeighteen. These numbers are preferred because they give the smallestnumber of radiating elements possible for a particular radius withoutproducing a current reversal in the elements.

In the case of Fig. 5, assuming that the radiating elements are of thesame length, a condition most practical and preferably to be used in allof the systems shown in Figs. 1 6, inclusive, then the electrical lengthof any one U section of line between radiating elements should be equalto one wavelength minus the length of a radiating element.

It will be understood that the invention is not limited to the precisearrangements shown and described, since various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the invention may be used to obtain uniform radiation in alldirections in the plane of the loop regardless of the angle of the loopwith respect to the horizontal. Of course, it will be appreciated thatthe principles of the invention are equally applicable to receivingantennae and that the invention is not limited solely to transmittingsystems.

It should also be understood that the term "1oop used in the appendedclaims is deemed to include either one continuous electrical connection,as shown in Figs. l, 3 and 5, or a plurality of spaced elements arrangedaround a circle and whose adjacent ends are insulated from one another,as shown in Figs. 4 and 6.

What is claimed is:

1. An antenna comprising a loop having a radius which corresponds to amaximum or a minimum of the function J1(21ra/ Where a is radius, i thewavelength, and J1(21ra/}\) is the first order Bessel function of thefirst kind with the argument (2nd/).

2. An antenna comprising a circular loop hava radius which correspondsto a maximum or a minimum of the function J1(21ra/ where a is theradius, A the wavelength, and J1(21ra/ is the first order Besselfunction of the first kind with the argument (2m/A), and a plurality ofserially connected condensers in said loop for tuning out, at leastpartially, the self-inductance of the loop, the lengths of the wiresections between condensers being not greater than onequarterwavelength.

3. An antenna comprising a circular loop hava radius which correspondsto a maximum or a minimum of the function J1(21ra/ where a is theradius, i the wavelength, and J1(21ra/ is the first order Besselfunction of the first kind with the argument (2m/i), and means seriallyconnected in said loop for providing substantially uniform currentdistribution.

4. An antenna comprising a circular horizontal loop having a diameterequal approximately to 0.60 wavelength, and means for producingsubstantially cophasal current in the antenna elements constituting theloop.

5. An antenna comprising a plurality of horizontal circular loops, oneabove the other, each having a radius which corresponds to a maximum ora minimum of the function J1(21ra/)\) where a is the radius, A thewavelength, and J1(21ra/ is the rst order Bessel function of the firstkind with the argument (21m/i), and means for producing substantiallycophasal current in the antenna elements constituting each loop.

6. An antenna comprising a plurality of concentric horizontal loops, inthe same plane, having, successively, respective radii of approximately0.29, .85 and 1.36 wavelengths, and means for energizing adjacent loopsout of phase, and the elements of each loop in such manner that thecurrent is substantially cophasal throughout the loop.

7. An antenna in accordance with claim 6, including a plurality ofserially connected condensers in each loop for providing substantiallyuniform current distribution, the sections of wire of each loop betweensuccessive condensers being not greater than one-quarter wavelength.

8. An antenna comprising a plurality of horizontal circular loops, oneabove the other, each having a radius which corresponds to a maximum ora minimum of the function J1(21ra/ where a is the radius, i thewavelength, and J1(2 ia/i) is the first order Bessel function of thefirst kind with the argument (21m/), and means for energizing said loopscophasally.

9. An antenna comprising a plurality of separated radiating elements,each not exceeding one-half wavelength, substantially in the form of acircle, and means for producing currents which flow in the samedirection around said circle in all of said elements, the radius of saidcircle corresponding to a maximum or a minimum of the function J1 21ra/where a is the radius, i the Wavelength, and J1(21ra/ is the first orderBessel function of the rst kind.

10. An antenna comprising a plurality of separated dipoles arrangedsubstantially in the form of a circle, each of said dipoles notexceeding onehalf the length of the communication wave, and a pair ofleads extending from the center of each dipole to high frequencyapparatus, whereby currents fiow in the same direction around saidcircle in all of said dipoles, the radius of said circle correspondingto a maximum or a minimum of the function J1(21ra/ where a is theradius, x the Wavelength, and J1(21ra/A) is the iirst order Besselfunction of the rst kind.

l1. An antenna comprising a horizontal loop having a radius which issubstantially equal to 0.85 times the length of the communication wave,I

and means for producing substantially cophasal current in the antennaelements constituting the loop.

12. An antenna comprising a horizontal loop having a radius which issubstantially equal to 1.36 times the length of the communication wave,and means for producing substantially cophasal current in the antennaelements constituting the loop.

13. An antenna comprising a horizontal loop having a radius which issubstantially equal to 0.85 times the length of the communication wave,a plurality of spaced, serially connected condensers in said loop, thesections of loop between successive condensers having lengths notexceeding half the length of the operating Wave.

14. An antenna comprising a plurality of horizontal circular loops, oneabove the other, each having a radius which corresponds to a maximum ora minimum of the function J1(21ra/ where a is the radius, x thewavelength, and J1(21ra/ is the first order Bessel function of the rstkind with the argument (21m/7l), said loops being spaced at leastone-half wavelength apart, and means for energizing said loopscophasalln PHILIP S. CARTER.

